Gold produced with a cyanide-free thiosulphate process is adding value to a US gold operation. Roger Nicoll reports that the process incorporates patented technology developed through a collaboration between Barrick Gold Corporation and CSIRO.

The first gold bar produced with the thiosulphate process was poured in late 2014 at Barrick’s Goldstrike plant in Nevada, USA and operations are ramping up to recover gold from four million tonnes of stockpiled ore that was uneconomic to process by traditional methods.

CSIRO's Danielle Hewitt, who worked at the Barrick demonstration plant to develop and prove the Barrick-CSIRO technology, was on hand to see the first gold bar.

"This was a golden moment of more than 20 years in the making, including three years working with Barrick to refine the commercial process," Mrs Hewitt said.

"It's the culmination of years of hard work and a good example of how our partnership culture is manifesting itself on the ground," says Goldstrike General Manager Andy Cole.

"This was a huge initiative, and it would not have succeeded if it weren’t for the collaboration, trust and accountability that developed between our project team, CSIRO, the construction group and the Goldstrike operations team."

Thiosulphate has long been seen as a potential alternative to cyanide for liberating gold from ores, but until now it has proved difficult to master. Cyanide is highly toxic and an environmental hazard.

Yeonuk Choi, Danielle Hewitt and John Langhans with the first gold bar produced with the cyanide-free process.

Yeonuk Choi, Danielle Hewitt and John Langhans with the first gold bar produced with the cyanide-free process.

As part of the thiosulphate process at Goldstrike, gold-bearing ore is heated as a thick slurry of ore, air, water and limestone in large pressure chambers or autoclaves and then pumped into the new ‘resin-in-leach’ circuit that takes place inside large stainless steel tanks.

Within the tanks, the slurry interacts with thiosulfate and a fine, bead-like material called resin that collects the gold.

At full capacity, 13,400 tons of ore can be processed daily, with leaching taking place simultaneously in two sets of seven tanks.

The thiosulphate process will enable Barrick to contribute an average of 350 to 450 thousand ounces of gold each year to their operation, allowing the large plant to keep operating, preserving jobs and bringing much needed income to the State.

"Replacing cyanide with the non-toxic thiosulphate stands to reduce environmental risks and open other opportunities in countries where gold cyanidation is banned," says CSIRO Team Leader for Gold Processing, Dr Paul Breuer.

"Thiosulphate processes may also be viable for low-grade deposits or deep ore bodies, where in situ recovery would be safer for workers and the environment," Dr Breuer said.